span tag, vw/vh, %, px

Span Tag
The span tag is used to style a small part of text without breaking line. It is an inline element.

<span>text</span>
<p>I am learning <span style="color:red;">HTML</span> today.</p>

Only "HTML" becomes red color.
px, %, vw, vh (CSS Units)
These are used to set size, width, height, spacing.
px (Pixel):
Fixed size unit.

div {
  width: 200px;
}

200px = fixed size.
Does NOT change for screen size.
% (Percentage):
Relative to parent element.

div {
  width: 50%;
}

Takes 50% of parent width.
vw (Viewport Width):
Relative to screen width.

div {
  width: 50vw;
}

1vw = 1% of screen width.
50vw = half of screen width.
vh (Viewport Height):
Relative to screen height.

div {
  height: 100vh;
}

100vh = full screen height.