diff --git a/examples/simple.py b/examples/simple.py
index c3389441a..ac621befe 100644
--- a/examples/simple.py
+++ b/examples/simple.py
@@ -35,4 +35,4 @@ class MyApp(App):
         await self.call_later(get_markdown, "richreadme.md")
 
 
-MyApp.run(title="Simple App", log="textual.log")
+MyApp.run(title="Simple App", log="textual.log", css_file="theme.css")
diff --git a/examples/theme.css b/examples/theme.css
new file mode 100644
index 000000000..3f852c16f
--- /dev/null
+++ b/examples/theme.css
@@ -0,0 +1,7 @@
+Header {
+  border: solid #122233;
+}
+
+App > View > Widget {
+  display: none;
+}
diff --git a/src/textual/app.py b/src/textual/app.py
index 331c31563..fcea8f18d 100644
--- a/src/textual/app.py
+++ b/src/textual/app.py
@@ -2,7 +2,7 @@ from __future__ import annotations
 import os
 
 import asyncio
-from functools import partial
+
 from typing import Any, Callable, ClassVar, Type, TypeVar
 import warnings
 
@@ -21,6 +21,7 @@ from .geometry import Offset, Region
 from . import log
 from ._callback import invoke
 from ._context import active_app
+from .css.stylesheet import Stylesheet
 from ._event_broker import extract_handler_actions, NoHandler
 from .driver import Driver
 from .layouts.dock import DockLayout, Dock
@@ -66,6 +67,7 @@ class App(MessagePump):
         log: str = "",
         log_verbosity: int = 1,
         title: str = "Textual Application",
+        css_file: str | None = None,
     ):
         """The Textual Application base class
 
@@ -104,6 +106,10 @@ class App(MessagePump):
         self.bindings.bind("ctrl+c", "quit", show=False, allow_forward=False)
         self._refresh_required = False
 
+        self.stylesheet = Stylesheet()
+
+        self.css_file = css_file
+
         super().__init__()
 
     title: Reactive[str] = Reactive("Textual")
@@ -124,6 +130,9 @@ class App(MessagePump):
     def view(self) -> DockView:
         return self._view_stack[-1]
 
+    def load_css(self, filename: str) -> None:
+        pass
+
     def log(self, *args: Any, verbosity: int = 1, **kwargs) -> None:
         """Write to logs.
 
@@ -269,6 +278,13 @@ class App(MessagePump):
         log("---")
         log(f"driver={self.driver_class}")
 
+        try:
+            if self.css_file is not None:
+                self.stylesheet.read(self.css_file)
+                print(self.stylesheet.css)
+        except Exception:
+            self.panic()
+
         load_event = events.Load(sender=self)
         await self.dispatch_message(load_event)
         await self.post_message(events.Mount(self))
diff --git a/src/textual/css/model.py b/src/textual/css/model.py
index ea8d44391..71a208060 100644
--- a/src/textual/css/model.py
+++ b/src/textual/css/model.py
@@ -36,6 +36,18 @@ class Selector:
     selector: SelectorType = SelectorType.TYPE
     pseudo_classes: list[str] = field(default_factory=list)
 
+    @property
+    def css(self) -> str:
+        psuedo_suffix = "".join(f":{name}" for name in self.pseudo_classes)
+        if self.selector == SelectorType.UNIVERSAL:
+            return "*"
+        elif self.selector == SelectorType.TYPE:
+            return f"{self.name}{psuedo_suffix}"
+        elif self.selector == SelectorType.CLASS:
+            return f".{self.name}{psuedo_suffix}"
+        else:
+            return f"#{self.name}{psuedo_suffix}"
+
 
 @dataclass
 class Declaration:
@@ -50,3 +62,23 @@ class Declaration:
 class RuleSet:
     selectors: list[list[Selector]] = field(default_factory=list)
     styles: Styles = field(default_factory=Styles)
+
+    @classmethod
+    def selector_to_css(cls, selectors: list[Selector]) -> str:
+        tokens: list[str] = []
+        for selector in selectors:
+            if selector.combinator == CombinatorType.DESCENDENT:
+                tokens.append(" ")
+            elif selector.combinator == CombinatorType.CHILD:
+                tokens.append(" > ")
+            tokens.append(selector.css)
+        return "".join(tokens).strip()
+
+    @property
+    def css(self) -> str:
+        selectors = ", ".join(
+            self.selector_to_css(selector) for selector in self.selectors
+        )
+        declarations = "\n".join(f"    {line}" for line in self.styles.css_lines)
+        css = f"{selectors} {{\n{declarations}\n}}"
+        return css
diff --git a/src/textual/css/parse.py b/src/textual/css/parse.py
index 8d824bb75..5b489406e 100644
--- a/src/textual/css/parse.py
+++ b/src/textual/css/parse.py
@@ -76,7 +76,6 @@ def parse_rule_set(tokens: Iterator[Token], token: Token) -> Iterable[RuleSet]:
     if declaration.tokens:
         rule_set.styles.add_declaration(declaration)
 
-    print(rule_set)
     yield rule_set
 
 
@@ -87,16 +86,24 @@ def parse(css: str) -> Iterable[RuleSet]:
         token = next(tokens, None)
         if token is None:
             break
-        if token.name.startswith("selector_start_"):
+        if token.name.startswith("selector_start"):
             yield from parse_rule_set(tokens, token)
 
 
 if __name__ == "__main__":
     test = """
 .foo.bar baz:focus, #egg {
+    display: block
     visibility: visible;
     border: solid green !important;
-    outline: red
+    outline: red;
+    padding: 1 2;
+    margin: 5
 }"""
-    for obj in parse(test):
-        print(obj)
+
+    from .stylesheet import Stylesheet
+
+    stylesheet = Stylesheet()
+    stylesheet.parse(test)
+    print(stylesheet)
+    print(stylesheet.css)
diff --git a/src/textual/css/styles.py b/src/textual/css/styles.py
index 0b8eafdbf..e5ada20d8 100644
--- a/src/textual/css/styles.py
+++ b/src/textual/css/styles.py
@@ -1,14 +1,16 @@
 from __future__ import annotations
 
 from dataclasses import dataclass, field
-from typing import cast, TYPE_CHECKING
+from typing import cast, Sequence, TYPE_CHECKING
 
 from rich import print
+import rich.repr
 from rich.color import ANSI_COLOR_NAMES, Color
 
 from ._error_tools import friendly_list
+from ..geometry import Spacing, SpacingDimensions
 from .tokenize import Token
-from .types import Visibility
+from .types import Display, Visibility
 
 if TYPE_CHECKING:
     from .model import Declaration
@@ -21,68 +23,347 @@ class DeclarationError(Exception):
 
 
 VALID_VISIBILITY = {"visible", "hidden"}
+VALID_DISPLAY = {"block", "none"}
 VALID_BORDER = {"rounded", "solid", "double", "dashed", "heavy", "inner", "outer"}
 
 
+NULL_SPACING = Spacing(0, 0, 0, 0)
+
+
+class _BoxSetter:
+    def __set_name__(self, owner, name):
+        self.internal_name = f"_{name}"
+        _type, edge = name.split("_")
+        self._type = _type
+        self.edge = edge
+
+    def __get__(self, obj: Styles, objtype=None) -> tuple[str, str] | None:
+        value = getattr(obj, self.internal_name)
+        if value is None:
+            return None
+        else:
+            _type, color = value
+            return (_type, color.name)
+
+    def __set__(
+        self, obj: Styles, border: tuple[str, str] | None
+    ) -> tuple[str, Color] | None:
+        if border is None:
+            new_value = None
+        else:
+            _type, color = border
+            if isinstance(color, Color):
+                new_value = (_type, color)
+            else:
+                new_value = (_type, Color.parse(color))
+        setattr(obj, self.internal_name, new_value)
+        return new_value
+
+
 @dataclass
 class Styles:
 
-    visibility: Visibility | None = None
+    _display: Display | None = None
+    _visibility: Visibility | None = None
 
-    border_top: tuple[str, Color] | None = None
-    border_right: tuple[str, Color] | None = None
-    border_bottom: tuple[str, Color] | None = None
-    border_left: tuple[str, Color] | None = None
+    _padding: Spacing | None = None
+    _margin: Spacing | None = None
 
-    outline_top: tuple[str, Color] | None = None
-    outline_right: tuple[str, Color] | None = None
-    outline_bottom: tuple[str, Color] | None = None
-    outline_left: tuple[str, Color] | None = None
+    _border_top: tuple[str, Color] | None = None
+    _border_right: tuple[str, Color] | None = None
+    _border_bottom: tuple[str, Color] | None = None
+    _border_left: tuple[str, Color] | None = None
 
-    important: set[str] = field(default_factory=set)
+    _outline_top: tuple[str, Color] | None = None
+    _outline_right: tuple[str, Color] | None = None
+    _outline_bottom: tuple[str, Color] | None = None
+    _outline_left: tuple[str, Color] | None = None
+
+    _important: set[str] = field(default_factory=set)
+
+    @property
+    def display(self) -> Display:
+        return self._display or "block"
+
+    @display.setter
+    def display(self, display: Display) -> None:
+        if display not in VALID_DISPLAY:
+            raise ValueError(f"display must be one of {friendly_list(VALID_DISPLAY)}")
+        self._display = display
+
+    @property
+    def visibility(self) -> Visibility:
+        return self._visibility or "visible"
+
+    @visibility.setter
+    def visibility(self, visibility: Visibility) -> None:
+        if visibility not in VALID_VISIBILITY:
+            raise ValueError(
+                f"visibility must be one of {friendly_list(VALID_VISIBILITY)}"
+            )
+        self._visibility = visibility
+
+    @property
+    def padding(self) -> Spacing:
+        return self._padding or NULL_SPACING
+
+    @padding.setter
+    def padding(self, padding: SpacingDimensions) -> None:
+        self._padding = Spacing.unpack(padding)
+
+    @property
+    def margin(self) -> Spacing:
+        return self._margin or NULL_SPACING
+
+    @margin.setter
+    def margin(self, padding: SpacingDimensions) -> None:
+        self._margin = Spacing.unpack(padding)
+
+    @property
+    def border(
+        self,
+    ) -> tuple[
+        tuple[str, str] | None,
+        tuple[str, str] | None,
+        tuple[str, str] | None,
+        tuple[str, str] | None,
+    ]:
+        return (
+            self.border_top,
+            self.border_right,
+            self.border_bottom,
+            self.border_left,
+        )
+
+    @border.setter
+    def border(
+        self, border: Sequence[tuple[str, str] | None] | tuple[str, str] | None
+    ) -> None:
+        if border is None:
+            self._border_top = (
+                self._border_right
+            ) = self._border_bottom = self._border_left = None
+            return
+        if isinstance(border, tuple):
+            self.border_top = (
+                self.border_right
+            ) = self.border_bottom = self.border_left = border
+            return
+        count = len(border)
+        if count == 1:
+            self.border_top = (
+                self.border_right
+            ) = self.border_bottom = self.border_left = border[0]
+        elif count == 2:
+            self.border_top = self.border_right = border[0]
+            self.border_bottom = self.border_left = border[1]
+        elif count == 4:
+            top, right, bottom, left = border
+            self.border_top = top
+            self.border_right = right
+            self.border_bottom = bottom
+            self.border_left = left
+        else:
+            raise ValueError("expected 1, 2, or 4 values")
+
+    border_top = _BoxSetter()
+    border_right = _BoxSetter()
+    border_bottom = _BoxSetter()
+    border_left = _BoxSetter()
+
+    outline_top = _BoxSetter()
+    outline_right = _BoxSetter()
+    outline_bottom = _BoxSetter()
+    outline_left = _BoxSetter()
+
+    def __rich_repr__(self) -> rich.repr.Result:
+        yield "display", self.display, "block"
+        yield "visibility", self.visibility, "visible"
+        yield "padding", self.padding, NULL_SPACING
+        yield "margin", self.padding, NULL_SPACING
+
+        yield "border_top", self.border_top, None
+        yield "border_right", self.border_right, None
+        yield "border_bottom", self.border_bottom, None
+        yield "border_left", self.border_left, None
+
+        yield "outline_top", self.outline_top, None
+        yield "outline_right", self.outline_right, None
+        yield "outline_bottom", self.outline_bottom, None
+        yield "outline_left", self.outline_left, None
+
+    @property
+    def css_lines(self) -> list[str]:
+        lines: list[str] = []
+        append = lines.append
+
+        def append_declaration(name: str, value: str) -> None:
+            if name in self._important:
+                append(f"{name}: {value} !important;")
+            else:
+                append(f"{name}: {value};")
+
+        if self._display is not None:
+            append_declaration("display", self._display)
+
+        if self._visibility is not None:
+            append_declaration("visibility", self._visibility)
+
+        if self._padding is not None:
+            append_declaration("padding", self._padding.packed)
+
+        if self._margin is not None:
+            append_declaration("margin", self._margin.packed)
+
+        if (
+            self._border_top != None
+            and self._border_top == self._border_right
+            and self._border_right == self._border_bottom
+            and self._border_bottom == self._border_left
+        ):
+            _type, color = self._border_top
+            append_declaration("border", f"{_type} {color.name}")
+        else:
+
+            if self._border_top is not None:
+                _type, color = self._border_top
+                append_declaration("border-top", f"{_type} {color.name}")
+
+            if self._border_right is not None:
+                _type, color = self._border_right
+                append_declaration("border-right", f"{_type} {color.name}")
+
+            if self._border_bottom is not None:
+                _type, color = self._border_bottom
+                append_declaration("border-bottom", f"{_type} {color.name}")
+
+            if self._border_left is not None:
+                _type, color = self._border_left
+                append_declaration("border-left", f"{_type} {color.name}")
+
+        if (
+            self._outline_top != None
+            and self._outline_top == self._outline_right
+            and self._outline_right == self._outline_bottom
+            and self._outline_bottom == self._outline_left
+        ):
+            _type, color = self._outline_top
+            append_declaration("outline", f"{_type} {color.name}")
+        else:
+
+            if self._outline_top is not None:
+                _type, color = self._outline_top
+                append_declaration("outline-top", f"{_type} {color.name}")
+
+            if self._outline_right is not None:
+                _type, color = self._outline_right
+                append_declaration("outline-right", f"{_type} {color.name}")
+
+            if self._outline_bottom is not None:
+                _type, color = self._outline_bottom
+                append_declaration("outline-bottom", f"{_type} {color.name}")
+
+            if self._outline_left is not None:
+                _type, color = self._outline_left
+                append_declaration("outline-left", f"{_type} {color.name}")
+
+        return lines
 
     def error(self, name: str, token: Token, msg: str) -> None:
-        raise DeclarationError(name, token, msg)
+        line, col = token.location
+        raise DeclarationError(name, token, f"{msg} (line {line + 1}, col {col + 1})")
 
     def add_declaration(self, declaration: Declaration) -> None:
 
-        print(declaration)
         if not declaration.tokens:
             return
         process_method = getattr(self, f"process_{declaration.name.replace('-', '_')}")
         tokens = declaration.tokens
         if tokens[-1].name == "important":
             tokens = tokens[:-1]
-            self.important.add(declaration.name)
+            self._important.add(declaration.name)
         if process_method is not None:
             process_method(declaration.name, tokens)
 
-    def _parse_border(self, tokens: list[Token]) -> tuple[str, Color]:
-        color = Color.default()
-        border_type = "solid"
+    def process_display(self, name: str, tokens: list[Token]) -> None:
         for token in tokens:
             location, name, value = token
             if name == "token":
+                value = value.lower()
+                if value in VALID_DISPLAY:
+                    self._display = cast(Display, value)
+                else:
+                    self.error(
+                        name,
+                        token,
+                        f"invalid value for display (received {value!r}, expected {friendly_list(VALID_DISPLAY)})",
+                    )
+            else:
+                self.error(name, token, f"invalid token {value!r} in this context")
+
+    def process_visibility(self, name: str, tokens: list[Token]) -> None:
+        for token in tokens:
+            location, name, value = token
+            if name == "token":
+                value = value.lower()
+                if value in VALID_VISIBILITY:
+                    self._visibility = cast(Visibility, value)
+                else:
+                    self.error(
+                        name,
+                        token,
+                        f"invalid value for visibility (received {value!r}, expected {friendly_list(VALID_VISIBILITY)})",
+                    )
+            else:
+                self.error(name, token, f"invalid token {value!r} in this context")
+
+    def _process_space(self, name: str, tokens: list[Token]) -> None:
+        space: list[int] = []
+        append = space.append
+        for token in tokens:
+            location, toke_name, value = token
+            if toke_name == "number":
+                append(int(value))
+            else:
+                self.error(name, token, f"unexpected token {value!r} in declaration")
+        if len(space) not in (1, 2, 4):
+            self.error(
+                name, tokens[0], f"1, 2, or 4 values expected (received {len(space)})"
+            )
+        setattr(self, f"_{name}", Spacing.unpack(cast(SpacingDimensions, tuple(space))))
+
+    def process_padding(self, name: str, tokens: list[Token]) -> None:
+        self._process_space(name, tokens)
+
+    def process_margin(self, name: str, tokens: list[Token]) -> None:
+        self._process_space(name, tokens)
+
+    def _parse_border(self, name: str, tokens: list[Token]) -> tuple[str, Color]:
+        color = Color.default()
+        border_type = "solid"
+        for token in tokens:
+            location, token_name, value = token
+            if token_name == "token":
                 if value in ANSI_COLOR_NAMES:
                     color = Color.parse(value)
                 elif value in VALID_BORDER:
                     border_type = value
                 else:
                     self.error(name, token, f"unknown token {value!r} in declaration")
-            elif name == "color":
+            elif token_name == "color":
                 color = Color.parse(value)
             else:
                 self.error(name, token, f"unexpected token {value!r} in declaration")
         return (border_type, color)
 
     def _process_border(self, edge: str, name: str, tokens: list[Token]) -> None:
-        border = self._parse_border(tokens)
-        setattr(self, f"border_{edge}", border)
+        border = self._parse_border("border", tokens)
+        setattr(self, f"_border_{edge}", border)
 
     def process_border(self, name: str, tokens: list[Token]) -> None:
-        border = self._parse_border(tokens)
-        self.border_top = self.border_right = border
-        self.border_bottom = self.border_left = border
+        border = self._parse_border("border", tokens)
+        self._border_top = self._border_right = border
+        self._border_bottom = self._border_left = border
 
     def process_border_top(self, name: str, tokens: list[Token]) -> None:
         self._process_border("top", name, tokens)
@@ -97,13 +378,13 @@ class Styles:
         self._process_border("left", name, tokens)
 
     def _process_outline(self, edge: str, name: str, tokens: list[Token]) -> None:
-        border = self._parse_border(tokens)
-        setattr(self, f"outline_{edge}", border)
+        border = self._parse_border("outline", tokens)
+        setattr(self, f"_outline_{edge}", border)
 
     def process_outline(self, name: str, tokens: list[Token]) -> None:
-        border = self._parse_border(tokens)
-        self.outline_top = self.outline_right = border
-        self.outline_bottom = self.outline_left = border
+        border = self._parse_border("outline", tokens)
+        self._outline_top = self._outline_right = border
+        self._outline_bottom = self._outline_left = border
 
     def process_outline_top(self, name: str, tokens: list[Token]) -> None:
         self._process_outline("top", name, tokens)
@@ -117,18 +398,15 @@ class Styles:
     def process_outline_left(self, name: str, tokens: list[Token]) -> None:
         self._process_outline("left", name, tokens)
 
-    def process_visibility(self, name: str, tokens: list[Token]) -> None:
-        for token in tokens:
-            location, name, value = token
-            if name == "token":
-                value = value.lower()
-                if value in VALID_VISIBILITY:
-                    self.visibility = cast(Visibility, value)
-                else:
-                    self.error(
-                        name,
-                        token,
-                        f"invalid value for visibility (received {value!r}, expected {friendly_list(VALID_VISIBILITY)})",
-                    )
-            else:
-                self.error(name, token, f"invalid token {value!r} in this context")
+
+if __name__ == "__main__":
+    styles = Styles()
+
+    styles.display = "none"
+    styles.visibility = "hidden"
+    styles.border = ("solid", "rgb(10,20,30)")
+    styles.outline_right = ("solid", "red")
+
+    from rich import print
+
+    print(styles)
diff --git a/src/textual/css/stylesheet.py b/src/textual/css/stylesheet.py
new file mode 100644
index 000000000..72e15204f
--- /dev/null
+++ b/src/textual/css/stylesheet.py
@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+import rich.repr
+
+from .model import RuleSet
+from .parse import parse
+
+
+class StylesheetError(Exception):
+    pass
+
+
+@rich.repr.auto
+class Stylesheet:
+    def __init__(self) -> None:
+        self.rules: list[RuleSet] = []
+
+    def __rich_repr__(self) -> rich.repr.Result:
+        yield self.rules
+
+    @property
+    def css(self) -> str:
+        return "\n\n".join(rule_set.css for rule_set in self.rules)
+
+    def read(self, filename: str) -> None:
+        try:
+            with open(filename, "rt") as css_file:
+                css = css_file.read()
+            del css_file
+        except Exception as error:
+            raise StylesheetError(f"unable to read {filename!r}; {error}") from None
+        try:
+            rules = list(parse(css))
+        except Exception as error:
+            raise StylesheetError(f"failed to parse {filename!r}; {error}") from None
+        self.rules.extend(rules)
+
+    def parse(self, css: str) -> None:
+        try:
+            rules = list(parse(css))
+        except Exception as error:
+            raise StylesheetError(f"failed to parse css; {error}") from None
+        self.rules.extend(rules)
diff --git a/src/textual/css/tokenize.py b/src/textual/css/tokenize.py
index 8b06521ef..f517e5679 100644
--- a/src/textual/css/tokenize.py
+++ b/src/textual/css/tokenize.py
@@ -45,7 +45,7 @@ expect_declaration_content = Expect(
     whitespace=r"\s+",
     comment_start=r"\/\*",
     percentage=r"\d+\%",
-    number=r"\d+\.?\d+",
+    number=r"\d+\.?\d*",
     color=r"\#[0-9a-f]{6}|color\[0-9]{1,3}\|rgb\([\d\s,]+\)",
     token="[a-zA-Z_-]+",
     string=r"\".*?\"",
@@ -82,7 +82,6 @@ def tokenize(code: str) -> Iterable[Token]:
         elif name == "eof":
             break
         expect = get_state(name, expect)
-        print(token)
         yield token
 
 
diff --git a/src/textual/css/tokenizer.py b/src/textual/css/tokenizer.py
index 8cddd1a88..83caf480c 100644
--- a/src/textual/css/tokenizer.py
+++ b/src/textual/css/tokenizer.py
@@ -74,15 +74,14 @@ class Tokenizer:
             if value is not None:
                 break
 
-        try:
-            return Token((line_no, col_no), name, value)
-        finally:
-            col_no += len(value)
-            if col_no >= len(line):
-                line_no += 1
-                col_no = 0
-            self.line_no = line_no
-            self.col_no = col_no
+        token = Token((line_no, col_no), name, value)
+        col_no += len(value)
+        if col_no >= len(line):
+            line_no += 1
+            col_no = 0
+        self.line_no = line_no
+        self.col_no = col_no
+        return token
 
     def skip_to(self, expect: Expect) -> Token:
         line_no = self.line_no
diff --git a/src/textual/css/types.py b/src/textual/css/types.py
index 234bc75e0..cfe44a46a 100644
--- a/src/textual/css/types.py
+++ b/src/textual/css/types.py
@@ -9,3 +9,4 @@ else:
 
 
 Visibility = Literal["visible", "hidden", "initial", "inherit"]
+Display = Literal["block", "none"]
diff --git a/src/textual/geometry.py b/src/textual/geometry.py
index 861e11fc0..73123a3fe 100644
--- a/src/textual/geometry.py
+++ b/src/textual/geometry.py
@@ -457,6 +457,16 @@ class Spacing(NamedTuple):
         """Bottom right space."""
         return (self.right, self.bottom)
 
+    @property
+    def packed(self) -> str:
+        top, right, bottom, left = self
+        if top == right == bottom == left:
+            return f"{top}"
+        if (top, right) == (bottom, left):
+            return f"{top}, {right}"
+        else:
+            return f"{top}, {right}, {bottom}, {left}"
+
     @classmethod
     def unpack(cls, pad: SpacingDimensions) -> Spacing:
         """Unpack padding specified in CSS style."""